What is the maximum operating altitude for the APU?

The maximum operating altitude for the Auxiliary Power Unit (APU) is a critical specification that determines its operational limits in different environments. The correct choice indicates that the APU can function at a maximum altitude of 37,000 feet while in flight and at 14,000 feet on the ground.

This distinction is important because the APU is crucial for providing electrical power and pneumatic air for engine starting and environmental control systems, especially during flight and while on the ground. The operational ceiling of 37,000 feet ensures that the APU can support aircraft systems even when operating near the upper limits of commercial flight, where maintaining power and system functionality is essential.

Furthermore, the ground operation ceiling of 14,000 feet reflects the practical limitations of the APU's ability to draw air for combustion and to operate effectively within thinner atmospheric layers found at higher altitudes. Understanding this specification helps ensure that aircraft operators can make informed decisions about the aircraft's systems in varying flight and ground conditions.